1. Field of the Invention
The present invention relates to a bearing apparatus, a spindle motor, and a disk drive apparatus.
2. Description of the Related Art
Hard disk apparatuses and optical disk apparatuses are typically provided with a spindle motor arranged to rotate a disk or disks about a center axis thereof. The spindle motor includes a stationary portion fixed to a housing of the disk drive apparatus, and a rotating portion arranged to rotate while supporting the disk(s). The spindle motor is arranged to produce a torque centered on the center axis by magnetic flux generated between the stationary and rotating portions, whereby the rotating portion is caused to rotate with respect to the stationary portion.
The stationary and rotating portions of the spindle motor are joined to each other through a bearing apparatus. In recent years, in particular, spindle motors have often been provided with a bearing apparatus in which a lubricating fluid is arranged between the stationary and rotating portions. JP-A 2002-5171, for example, describes an example of such a bearing apparatus using the lubricating fluid. In the bearing apparatus described in JP-A 2002-5171, the lubricating fluid is arranged to fill a gap between a shaft and a sleeve which are rotatably supported with respect to each other.
The bearing apparatus described in JP-A 2002-5171 includes a radial dynamic pressure bearing portion and a pumping action portion. The bearing apparatus having such a structure has a problem in that, when it is desirable to limit the axial dimension of the bearing apparatus, both the axial dimension of the radial dynamic pressure bearing portion and that of the pumping action portion is not sufficient enough to allow both the radial dynamic pressure bearing portion and the pumping action portion to both exhibit a sufficient performance.
In addition, the pumping action portion may sometimes introduce air bubbles into the lubricating fluid when pumping the lubricating fluid. If the air bubbles introduced into the lubricating fluid are accumulated in the vicinity of a thrust dynamic pressure bearing portion or the radial dynamic pressure bearing portion, generation of a dynamic pressure in the lubricating fluid may be hindered. If this happens, a sufficient supporting force may not be obtained between the shaft and the sleeve to allow the bearing apparatus to maintain a sufficient rotation performance.
Conventional hard disk apparatuses and optical disk apparatuses are typically provided with a spindle motor arranged to rotate a disk or disks about a center axis thereof. The spindle motor includes a stationary portion fixed to a housing of the apparatus, and a rotating portion arranged to rotate while supporting the disk(s). The spindle motor is arranged to produce a torque centered on the center axis by magnetic flux generated between the stationary and rotating portions, whereby the rotating portion is caused to rotate with respect to the stationary portion.
The stationary and rotating portions of the spindle motor are joined to each other through a bearing apparatus. In recent years, in particular, spindle motors have often been provided with a bearing apparatus in which a lubricating fluid is arranged between the stationary and rotating portions. JP-A 2002-5171, for example, describes an example of such a bearing apparatus including the lubricating fluid. In the bearing apparatus described in JP-A 2002-5171, the lubricating fluid is arranged to fill a gap between a shaft and a sleeve which are rotatably supported with respect to each other. Meanwhile, JP-A 2009-8200 describes a fluid bearing apparatus having a lubricating fluid arranged therein.
In some bearing apparatuses including the lubricating fluid, a labyrinth seal, i.e., an extremely small gap, is defined between a surface of the lubricating fluid and an exterior space. The labyrinth seal limits entry and exit of a gas between the exterior space and a vicinity of the surface of the lubricating fluid, thereby reducing evaporation of the lubricating fluid.
However, the axial dimension of the bearing apparatus is increased when the labyrinth seal is defined by a rotating member and a shaft of a stationary portion. Moreover, when a reduction in the axial dimension of the bearing apparatus is to be achieved with the labyrinth seal defined by the rotating member and the shaft, each of the labyrinth seal and a fixing range over which the shaft and another member are fixed to each other needs to be shortened in an axial direction. This makes it difficult to improve the strength with which the shaft and the other member are fixed to each other and performance of the labyrinth seal.